If you are unable to send or receive email when connecting to the LTE service, then the following steps should help.
Firstly, you need to confirm that the email address itself is ok. You can do this by logging into it via webmail by going to the email’s site (such as https://www.gmail.com) or by using a third party site that allows access (such as https://mail2web.com/)
Secondly, you need to check that your email account is set up correctly. The incoming and outgoing mail servers may be incorrect in whatever application you are using. The Incoming mail server should remain the one you were using before, but the outgoing mail server should be set to smtp.imagine.ie